Harmonic analysis of force platform data in normal and cerebral palsy gait

Background. Examination of force platform data during gait is usually carried out in the time domain and is limited to selected points on the force–time graphs. Harmonic analysis allows examination of the whole waveform and has a greater potential for assessing the effects of treatment options. Therefore, the objectives of this study were to show the benefits of using harmonic analysis to determine the variability and symmetry of force platform data in normal and cerebral palsy gait. Methods. Harmonic analysis was carried out on the foot to ground reaction force data recorded from a group of cerebral palsy children and a matched control group when they walked at their preferred walking speed. Statistical tests were used to assess this frequency domain data and to validate the reconstructed force–time curves. Findings. The differences in the frequency domain parameters between the cerebral palsy and control groups were significant. The mediolateral force was the most variable and asymmetric parameter in the control group. Cerebral palsy gait was more variable and more asymmetric than normal gait. Interpretation. This study has shown that the force platform data derived from clinical gait analysis can reveal more useful information in the frequency domain than the limited time domain information commonly used for analysing this type of data.